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Rex::Encoder::Alpha2::AlphaMixed

Public Class Methods

gen_decoder(reg, offset) click to toggle source
# File lib/rex/encoder/alpha2/alpha_mixed.rb, line 44
def self.gen_decoder(reg, offset)
        decoder =
                 gen_decoder_prefix(reg, offset) +
                 "jA" +          # push 0x41
                 "X" +           # pop eax
                 "P" +           # push eax
                 "0A0" +         # xor byte [ecx+30], al
                 "A" +           # inc ecx                        <---
                 "kAAQ" +        # imul eax, [ecx+42], 51 -> 10       |
                 "2AB" +         # xor al, [ecx + 42]                 |
                 "2BB" +         # xor al, [edx + 42]                 |
                 "0BB" +         # xor [edx + 42], al                 |
                 "A" +           # inc ecx                            |
                 "B" +           # inc edx                            |
                 "X" +           # pop eax                            |
                 "P" +           # push eax                           |
                 "8AB" +         # cmp [ecx + 42], al                 |
                 "uJ" +          # jnz short -------------------------
                 "I"             # first encoded char, fixes the above J

        return decoder
end
gen_decoder_prefix(reg, offset) click to toggle source
# File lib/rex/encoder/alpha2/alpha_mixed.rb, line 10
def self.gen_decoder_prefix(reg, offset)
        if (offset > 32)
                raise "Critical: Offset is greater than 32"
        end

        # use inc ebx as a nop here so we still pad correctly
        if (offset <= 16)
                nop = 'C' * offset
                mod = 'I' * (16 - offset) + nop + '7QZ'    # dec ecx,,, push ecx, pop edx
                edxmod = 'J' * (17 - offset)
        else
                mod = 'A' * (offset - 16)
                nop = 'C' * (16 - mod.length)
                mod << nop + '7QZ'
                edxmod = 'B' * (17 - (offset - 16))
        end
        regprefix = {
                'EAX'   => 'PY' + mod,                         # push eax, pop ecx
                'ECX'   => 'I' + mod,                          # dec ecx
                'EDX'   =>  edxmod + nop + '7RY',                       # dec edx,,, push edx, pop ecx
                'EBX'   => 'SY' + mod,                         # push ebx, pop ecx
                'ESP'   => 'TY' + mod,                         # push esp, pop ecx
                'EBP'   => 'UY' + mod,                         # push ebp, pop ecx
                'ESI'   => 'VY' + mod,                         # push esi, pop ecx
                'EDI'   => 'WY' + mod,                         # push edi, pop ecx
        }

        reg.upcase!
        if (not regprefix.keys.include? reg)
                raise ArgumentError.new("Invalid register name")
        end
        return regprefix[reg]
end

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